This invention relates generally to golf balls, and more particularly to golf balls having a fused wound layer and a method for forming such balls.
Conventional golf balls can be divided into two general types of groups: solid balls or wound balls (also known as three piece balls). The difference in play characteristics resulting from these different types of constructions can be quite significant. Balls having a solid construction are generally most popular with the average, recreational golfer because they provide a very durable ball while also providing maximum distance. Solid balls are generally made with a single solid core usually made of a cross linked rubber, which is enclosed by a cover material. Typically the solid core is made of polybutadiene which is chemically crosslinked with zinc diacrylate and/or similar crosslinking agents and is covered by a tough, cut-proof blended cover. The cover is generally a material such as SURLYN(copyright), which is a trademark for an ionomer resin produced by DuPont de Nemours and Company. The combination of the core and cover materials provide a xe2x80x9chardxe2x80x9d ball that is virtually indestructible by golfers. Further, such a combination imparts a high initial velocity to the ball which results in increased distance. Because these materials are very rigid, solid balls can have a hard xe2x80x9cfeelxe2x80x9d when struck with a club. Likewise, due to their construction, these balls have a relatively low spin rate which provides greater distance.
At the present time, the wound ball remains the preferred ball of the more advanced player due to spin and feel characteristics. Wound balls typically have either a spherical solid rubber or liquid center around which many yards of a stretched elastic thread are wound forming a wound core. The wound core is then covered with a durable cover material such as a SURLYN(copyright) or similar material or a softer cover, such as Balata or polyurethane. Wound balls are generally softer and provide more spin, which enable a skilled golfer to have more control over the ball""s flight and position. Particularly, with approach shots onto the green, the high spin rate of soft, wound balls enable the golfer to stop the ball very near its landing position.
To make wound golf balls, manufacturers use winding machines to stretch the threads to various degrees of elongation during the winding process without subjecting the threads to unnecessary incidents of breakage. Generally, as the elongation and the winding tension increases, the compression and initial velocity of the ball increases. Thus, a more resilient wound ball is produced, which is desirable.
Generally, the prior art has been directed to making wound golf ball cores and golf balls using single-ply or two-ply polyisoprene thread. The polyisoprene thread is wound onto the centers at elongations between about 500-1000%. The amount of thread required for a golf ball core is dependent on the elastic modulus of the thread in the elongated state. Elongated polyisoprene thread has an elastic modulus between 10 and 20 ksi. The resilience, compression, spin characteristics and other properties of the golf ball are dependent on many factors. One significant factor is the packing density (i.e., how well the thread packs during winding). The winding pattern, geometry and tension of the thread determine the packing density. For conventional golf balls, properties of the windings, such as resilience, modulus of elasticity, and density are not altered after winding. As a result, the resilience, compression, spin characteristics and other properties of the ball are partly set after winding and remain unalterable. However, in certain situations it is desirable to be able to alter the above-mentioned properties of the ball after winding has been completed.
Regardless of the form of the ball, players generally seek a golf ball that maximizes total game performance for their requirements. Therefore, in an effort to meet the demands of the marketplace, manufacturers strive to produce golf balls with a wide variety of performance characteristics to meet the players individual requirements. Thus, golf ball manufacturers are continually searching for new ways in which to provide golf balls that deliver the maximum performance for golfers of all skill levels. One such improved golf ball is the subject of the present invention.
The present invention is directed to a golf ball with a center; and at least one fused wound layer surrounding the center. The fused wound layer can be a cover layer or an inner layer. The wound layer is formed by at least one thread and adjacent portions of the thread are fused together. The thread can be continuous.
In one embodiment, the wound layer further comprises a first thread and a separate, second thread, wherein at least one of the threads is a fusible material and the other thread is non-fusible, or both are fusible so that portions of the wound layer are fused.
In one embodiment, at least one cover layer is formed around the wound layer. Generally, the cover layers are applied by compression molding, injection molding or casting cover material over the core.
In yet another embodiment, the ball further includes at least one intermediate layer between the wound layer and the cover layer. In an additional alternative embodiment, the ball includes two or more fused, wound layers, and the ball can include a separate cover or the outer surface can be formed by one of the wound layers.
In another embodiment, the fused wound layer forms the outer surface of the ball so that no separate cover is used.
In an additional embodiment, the wound layer includes a radially extending fused portion, which forms from about 10% to about 100% of the thickness of the wound layer.
The present invention is further directed to a method of forming a golf ball, the method comprising the steps of: winding a thread onto a center to form a wound layer; and fusing portions of the thread together.
In an alternative embodiment, the step of winding further includes applying tension to the thread.
Furthermore, the fusing is accomplished by applying heat alone or with pressure. As a result, the fused threads are chemically, physically, and/or mechanically changed. The step of applying heat may further include at least one of the following: compression molding, injection molding, compression and injection molding, or infrared heating. The heat can be applied simultaneously with forming the cover layer.
In one embodiment, the pre-fused diameter of the wound core is greater than the post-fused diameter of the wound core or ball.
The present invention is also directed to a method of forming a golf ball, wherein the method comprises the steps of: selecting a center; winding a thread onto the center to form a wound layer with at least one property; and altering the properties of a radially extending portion of the wound layer by applying heat after completing the winding step. The step of altering the properties of the wound layer can further include altering the density of the radially extending portion or altering the elongated state of the thread in the radially extending portion.